The so-called Precocene-1 (P1) and Precocene-2 (P2) are known substances isolated from natural sources. Bowers et al reported about the biological effects of P1 and P2 [W. S. Bowers, T. Ohta et al: Science 193, 542 (1976)]. On the basis of this biological activity it could be expected that P1 and P2 would be useful as a new-type pesticide causing no environmental pollution.
Several articles are published on the biological activity, mechanism of action and metabolism of precocenes. It is known that these compounds exhibit their action by damaging the juvenile hormone producing organ of insects, i.e. by special injury of the so-called "corpora allata". On testing the effects of the substances isolated from nature the correlation between the given biological group of effects and the 2H-chromene ring-system was studied. According to experimental results the character and strength of the activity of precocenes depends to a large extent on the pest species, the test method used and from the point of view of chemical structure probably on the number and position of the substituents of the aromatic ring, the strength of the double bond of the pyrane ring and on the electronic and steric parameters of the complete molecule [W. S. Bowers; Martinez-Paro, R.: Science 197 1369 (1977); H. Schooneveld: Experientia 35 363 (1979); W. S. Bowers; Pontif. Acad. Sci. Scr. Varia 41 129 (1976); G. T. Brooks et al: Nature 281 570 (1979); T. Ohta: Kagaku to Seibutsu 17(2) 92 (1979); T. Ohta: Konchu no Seiri to Kagaku 63 (1979); G. Matolcsy et al: Z. Naturforsch. 35b. 1449 (1980); G. T. Brooks et al: Proc. Br. Crop. Prot. Conf. Pests. Dis. 1 273 (1979); G. E. Pratt et al: Nature 284 320 (1980); D. M. Soderlund et al: J. Agr. Food Chem. 28(4) 724 (1980); D. A. Schooley et al: Pestic. Biochem. Physiol. 13(2) 95 (1980); A. P. Ottridge et al: Pestic. Sci. 12(3) 245 (1981)].
As a result of the above research work a number of derivatives being more active than P1 and P2 occuring in nature were obtained, e.g. 6-methoxy-7-ethoxy-2,2-dimethyl-2H-chromene (Precocene 3, P3, 3623) which is ten times more effective than P2.
In the published articles and patent specifications relatively few analogue compounds - about 80-100 derivatives - are disclosed, although the precise study of correlations between biological activity and chemical structure and the selection of the most active derivatives would require much more compounds. This is probably due to the fact that the known synthesis are very complicated.
According to prior art [CHROMENES CHROMANONES and CHROMONES, Edited by G. P. Ellis: John Wiley and Sons London, pages 43-63, (1977)] several routes are known for the preparation of 2H-chromene derivatives, the said routes being independent from each other. The majority of these methods is used for the preparation of P1 and P2 and analogues thereof [W. S. Bowers, T. Ohta: Chem. Pharm. Bull. 25(9) 2788 (1977); D. J. Gale, J. P. K. Wilshire: J. Text. Inst. 12 525 (1979); W. Biernacki, W. Sobotka: Polish J. Chem. 53 2275 (1979); 54 2239 (1980); G. Cardillio et al: Tetr. Lett. 27 2545 (1979); J. Chem. Soc. Shem. Comm. 836 (1979); F. Camps, et al: Tetr. Lett. 40 3901 (1979); 21 2361 (1980); J. Het. Chem. 17 207 and 1377 (1980); Tsukayama et al: Heterocycles 16(6) 955 (1981 ); A. Banerji, N. C. Goomer: Ind. J. Chem. 20B 144 (1981)].
The following patent specifications are published in this field German Federal Republic patent No. 2,639,671; U.S. Pat. No. 4,162,326; Japanese patent Nos. 73121/79, 15,411/80, 40,637/80 and 43,039/80.
The common feature of the said patent specifications and other publications is that although different synthesis routes are used the preparation of each analogue compound constitutes a specific problem and requires the use of different starting materials.
Thus according to German Federal Republic patent No. 2,639,671 and Japanese patent Nos. 15,411/80 and 40,637/80 P2 is prepared from 3,4-dimethoxy-phenol and P3 being ten times more active from 3-ethoxy-4-methoxy-phenol and the industrial scale production of the said starting materials in a sufficient amount and suitable purity constitutes a rather complicated problem per se.